The preferred configuration of a two handle pressure balanced tub/shower valve would have one handle controlling the temperature while the other controls the on/off and volume. There are currently no two handle pressure balanced tub/shower valves available due in part to the phenomenon of "temperature kick". Temperature kick occurs when the volume handle is throttled down to a low flow condition, typically less than about 0.15 gallons per minute. When this occurs, the pressure in the valve from the shut off to the inlets is approximately the same. If there is a pressure imbalance between the hot and cold water, for instance if the hot water is 5 psi greater than the cold water, the pressure at the outlet would be higher than the cold water inlet pressure as the hot water pressure would dominate the cold water pressure. At this point, the flow exiting the valve would be full hot water. In a short period of time, about one minute, the body and shower riser would be filled with hot water. When the valve is turned back on, there is a blast of hot water coming out of the shower.
The same situation could occur if the pressures are equal, but one of the inlet openings is almost full open while the other is almost completely shut off. If it were desired to shower at a water temperature of 110.degree. F., when the cold water temperature is 50.degree. F. and the hot water temperature is 120.degree. F., the water opening would be almost totally biased to the hot water.
One way to prevent "temperature kick" is to ensure that the flow rate cannot be set at rates below about 0.15 gallons per minute. This is very difficult to achieve since most valves are infinitely adjustable across this range.
The present invention solves this problem by provision of a spring loaded stem extender which provides a "stop" and a ramped area which prevents extremely low flow rates.